As this kind of the magnetic disc device, there is known a hard disc drive (hereinafter referred to HDD). A magnetic head of the HDD floats over a layer of air that is produced by a kinetic pressure of the air caused by rotation of a magnetic disc, and is set up to read and write data in a state that the magnetic head is not directly in contact with the magnetic disc. However, because the HDD is configured to equalize an outer pressure value and an inner pressure value by means of a vent hole, the above kinetic pressure caused by barometric pressure (altitude) used changes and the magnetic head may be in contact with the magnetic disc.
Therefore, in a normal HDD, reliability is guaranteed in a warrantee range in which reliability is assured while preventing a magnetic head from being directly in contact with a magnetic disc on an entire area of the magnetic disc (barometric pressure generating a kinetic pressure bearable against impact and vibration caused during operation of the magnetic disc, for example, 0.6 atm (corresponding to an altitude of about 4,300 m) and 0.7 atm (corresponding to an altitude of about 3,000 m) when the temperature of HDD is 55 degree C. or more). For example, in a vehicle, a control device (hereinafter referred to as a vehicle control device) for controlling fuel injection is equipped in an in-vehicle navigation apparatus having an HDD equipped on it. For example, it is possible to stop operation of HDD to thereby protect the HDD in a case where a barometric pressure shown in barometric pressure information indicating a barometric pressure outside a vehicle and obtained from the vehicle control device via a controller-area-network (CAN). Although the barometric pressure is detected mainly to adjust injection amount of fuel, the barometric pressure information indicative of the barometric pressure may be obtained by the in-vehicle navigation apparatus via the CAN thereby reducing a number of parts composing of a barometric pressure sensor for detecting independently for the in-vehicle navigation apparatus.
In a related art, Patent Document 1, there is disclosed a technique of protecting an HDD in its entirety by stopping operation of the HDD under a shutdown state in a case where the HDD detects itself various environmental conditions of the HDD using various sensors and when environment specification is violated by eluding from a range of operable environment
Patent Document 1: Japanese Unexamined Patent Publication No. Hei. 11-213525.